Piezoelectric crystal



Aug. 18, 1936.- A. B. TRIPP g 2,051,524

PIEZOELECTRIC CRYSTAL AFiled April 27, 1935 www INSULATION mwm l M b '7% 8MM 9 1 y HcA/Zttorneg.

Augustus; B.

Tripp,

New York Schenectady, N1 Y., c assigner; to General ElectricfCompany,

a corporatioirol' Application Apfrii 27, 1935, ,serial No;L 185584.

'l Claims.

My-.invention relatestopiezo electric crystals and methods and"Y means quencythereof;

for adjusting the fre- It has for one ofits,`v objects` topincrease the facility withwhich the-.frequencyro piezo electric crystals is adjusted.

My Vinvention relates ymore, vparticularly to Vpiezo electric v crystals andrcrystalr apparatus` disclosed in my copending4 application s Serial- No.l 712,562,

led LFebruaryfZS, `1934i', and sentitlediPiezo electric crystals, of .which .mypresent application is a conf.

tinuation-infpart.

In that applicationA al piezo electric crystal is shown which is supported horizont'ally between two spaced electrodes .andiheld in place'fonone of said, electrodes-.by apinprojecting from the electrodeintogaminuteholefin.the crystal. This hole is 4placed at-` a., nodal pointI of the mechanical' vi-y bration of thea crystal vwhereby .the pirr has a minimum of effect upon the crystal frequency.

It, has-'.beenifound that.'l this hole, 'though situated at a nodal'point ofthemechanicalevibration oa the crystal, adjusting the frequencyfo aifords a. convenienti means'. for, f the. crystal, and that o by;a very, slight grindingat: an; edgezoff the-hole,

as by-v insertingl thepointedzfend of awire. into the hole and :rotatingf'thefwire-betweentthe fingers,

theffrequency.` offfthe fcrystalmay. be lowered over` a; considerable range.`

Thus in the use of piezoelectriccrystalsfand apparatus of the that Vthe V'crystal'.

type referred to if it be found afterproper adjustment of the electrodes of the cell in which it operates, does not produce the desired frequency, the crystal may be removed therefrom and ground slightly by a pin rolled between the ngers in the manner in dicated. If upon reinserting the crystal in the cell it be found lowered too much by this adjustment may be made ing between the crystal curate adjustment of the that the frequency has been grinding a subsequent by adjusting the spacelectrodes. Thus accrystal frequency may be effected with great facility by this alternate grinding at the hole with of the crystal electrode.

a pin and adjustment The novel features which I believe to be characteristic of my invention ticularity in the appended itself, however, together advantages thereof, may

reference to the following are set forth with parclaims. My invention with further objects and best be understood by description taken in connection with the accompanying drawing in which Fig. l is a cross-sectional view of a crystal cell and crystal utilized in accordance with my invention; Fig. 2 is an exploded view of the crystal (Cl. 17T-327') cell, -and.1ig; 3;"i's\.,illustrativeA off thel method tof grinding;of the.;crystal:; Referring to Fig. L-the sidewalls -offthe crystal cell edgewise of the crystalare formedgbyjthe; member lgcomprsinga suitable:A insulating ma- 5v terial, such, as aiphenolic: Vcondensation product,` and; which` is i shaped; to enclose t a space of.`` par.- allelopiped'. form. One electrode. ofafthe crystal cell comprises a.. conducting. member 2 which;A is attachedito the lower surface off-the member.Y l, 1o the opposite; electrode Y comprising; a conducting member afwhich is suspendedromrthe .upper wall ofthe crystal cell. Thisiupper wall ofthe crystal cellicomprises aplate t4, which rmaybe veither con+` ducting',or non-conducting, attachedto ,the mem-.. l5 ber,Y l` and'togwhicha conducting; internallyscrewthreaded collar f 5'; is' attachedg this. collar havingJ a1shoulden6.;which abutsagainst the lowerlsurface ofy thememberft, and a neck, whichfprojects just? through thefmember V4; theopening formed in the 1 member 4". by peening the (upper outer :edge-'ofthe neck. The bodyllsof the collar projects a considerable distance below the lower-surface of; the member 4. The electrodev member 3 'isz-externallyv screw-threaded4 into;` the 25 'Ifheipiezoelectric crystal Bz isimounted' between. 30,

the two electrodes.;andfhasa.,y minute, preferablyy cyl.indrioalzholeformedv at; the center, org-1 aty a', nodal point of mechanical vibration thereof. hole is in line with a somewhat smaller hole in the lower electrode. The crystal is held in posiv 35 tion on the lower electrode by means of a pin I0 having a cylindrical head which is in the hole in the crystal, and the body of which projects intor the hole in the lower electrode. This pin may be of any suitable material,V preferably metal.

This arrangement of members is best illustrated in Fig. 2. The upper wall 4 of the crystal cell, having the collar 5 peened therein is provided with screw holes l I in alignment with corresponding holes I2 in the member l, similar holes I3 45 being provided in the lower crystal electrode 2 whereby those members are attached by means of screws to the broadside faces of the member l. The lower portion of the member 3 is seen to be of somewhat larger diameter` than the upper 50 screw-threaded portion thereof and is of sufficient diameter to present a broadside surface which substantially covers or exceeds the surface of the crystal.

Itis necessary in a device of this kind, particu- 55 This. collar isY sec'zurediln 2-0 larly when used on aircraft, to restrain the crystal 8 against longitudinal movement within its enclosure thereby to prevent vibrating surfaces of the crystal from coming into contact with the xed members of the crystal cell. It has been found that the pin l arranged in the minute opening at the nodal point of the crystal is a. very advantageous manner of effecting this result. The hole in the crystal may be so small that it has little or no effect upon the characteristics of the crystal, such as the temperature coefficient, although it has been found that it reduces the crystal frequency. 'Ihe head of the pin l0 is of slightly smaller diameter than the hole 9 so that a slight clearance is present about the head to avoid cracking of the crystal due to changes in temperature. This head is also of about one-half the thickness of the crystal so that it has practically no effect upon the operation of the crystal.

` AThe-shortest internal dimension of the crystal cell is longer than the longestdimension ofthe crystal so that no part of the crystal ever touches a side `wall of the cell. Y.

Fig. 3 illustrates more particularly the method of adjusting the frequency of the crystal. The crystal is removed from the cell in which it is employed, laid upon aplate I4, and the point of a small pin l5 inserted in the hole 9. vBy rolling the pinl5 between the fingers the upper edge of the hole 9 may be slightly ground. This pin may, for example, comprise the sharpened end of a piece of wire of larger diameter than the hole, which ordinarily vis of about a millimeter and a half in diameter. Carborundum and water may, if desired, be used as an abrasive. 'Ihis grinding may be sufficient substantially to lower the frequency of the crystal. 'Ihe crystal may then be reinserted in the cell and if the frequency be too low the final adjustment may be made by rotating the electrode 3, thereby to adjust the air gap between the crystal and electrode. 'I'he crystals in `connection with which my present invention may be employed may be adapted for operationat any desired frequency including frequencies extending from 100 kilocycles to 15,000 kilocycles or higher.

It will be understood that my invention may be used in connection with crystals of X, Y, and other desired cuts and that they may be of rectangular, disk, triangular or other geometrical shape. w Y A What I claim as new and desire to secure by Letters Patent of the United States, is:

1. The method of lowering the frequency of a piezo electric crystal having a hole therein which includes grinding at the edges of the hole.

2. 'I'he method of lowering the frequency of a piezo electric crystal having a hole therein at a nodal point of mechanical vibration which includes grinding at the edges of the hole.

3. The method of lowering the frequency of a piezo electric crystal having a minute hole therein which includes inserting in said hole an instrument so shaped relative to the hole that it rides upon the edges of the hole at the entrance end of the crystal, and rotating said instrument to Wear away said edge.

4. The method of adjusting the frequency of a piezo electric crystal having a minute hole therein whereby it is retained in position between two variably spaced electrodes4 which includes alternately grinding at an edge of said hole, and adjusting the spacing between said electrodes until the desired frequency is obtained.

5. The method of adjusting the frequencyof a piezo electric crystal having a minute hole therein whereby it is retained in position between two variably spaced electrodes, which includes rough adjusting said frequency by removing the crystal from said electrodes and grinding at the edge of said hole until a frequencyl approximating the desired frequency is obtained, and `then replacing the crystal between said electrodes and adjusting the spacing between the electrodes until the desiredfrequency is obtained.

6. The method of lowering the natural frequency of a piezo electric crystal having anodal point of mechanical vibration which includes grinding olf a portion of the crystal in proximity to said nodal point.

7. The method of adjusting the natural frequency of a piezo electric crystal which is retained in position between two variable spaced electrodes and Vwhich has' a natural frequency of mechanical vibration which is higher than that desired which includes alternately grinding olf a portion of the crystal in proximity to a nodal point of mechanical vibration and adjusting the spacing between the electrodes until the desired frequency-is obtained.

Y AUGUSTUS B. TRIPP. 

